Curable compositions containing polymerizable monomers and radical polymerization initiators are widely used for dental curable compositions for use as dental cements, dental adhesives, composite resins, self-adhesive composite resins, sealants, dental autopolymerizing resins, etc.
Radical polymerization initiators are broadly classified into photopolymerization initiators and chemical polymerization initiators, and in recent years, dual cure products including both of them have been widely used in clinical practice. Among these radical polymerization initiators, chemical polymerization initiators are usually composed of a combination of an oxidizing agent and a reducing agent. When these oxidizing agent and reducing agent are mixed, a so-called redox reaction occurs to generate radicals, so that a polymerization reaction is initiated to promote the curing of a curable composition. A dental composition containing a redox polymerization initiator is usually separated into a composition containing an oxidizing agent and a composition containing a reducing agent for storage, and these compositions are mixed together just before use.
Compositions containing acidic components are usually used for dental curable compositions when they are used as dental cements, dental adhesives, self-adhesive composite resins, sealants, etc. that require adhesion to adherends. As redox polymerization initiators used in such compositions containing acidic components, radical polymerization initiators containing copper compounds have recently been proposed.
For example, Patent Literature 1 proposes a redox initiator containing a barbituric acid or thiobarbituric acid, a peroxodisulfate and/or peroxodiphosphate compound, a sulfinic acid compound, and a copper compound. Patent Literature 2 proposes a two-component initiator system including a hydroperoxide with a specific structure, a thiourea derivative, and a copper compound as an accelerator.
It is generally known that copper compounds are discolored and turned black by hydrogen sulfide produced by cariogenic bacteria in an oral environment. It is thus desirable to add traces of copper compounds for use in dental compositions.
According to the present inventors' studies, the redox initiator described in Patent Literature 1 has a drawback that even only use of a sulfinic acid compound and a copper compound can initiate a curing reaction, but in that case, the copper compound must be added at a high concentration to ensure the curability of the resulting composition and thus the composition is more susceptible to discoloration by hydrogen sulfide in an oral environment. The two-component initiator system described in Patent Literature 2 also has a drawback that at least a certain amount of a copper compound must be added to ensure the curability of the resulting composition and thus the composition is more susceptible to discoloration by hydrogen sulfide in an oral environment.